8-Speed Transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes three planetary gear sets having six torque-transmitting devices, a fixed interconnection and a grounded member. The powertrain includes an engine and torque converter that is selectively connected to at least one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The six torque-transmitting devices provide interconnections between various gear members, the transmission housing and with the input member, and are operated in combinations of three to establish at least eight forward speed ratios and at least one reverse speed ratio.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 60/909,145, filed Mar. 30, 2007, and which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a power transmission having threeplanetary gear sets that are controlled by six torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five- or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

The present invention provides an improved transmission having threeplanetary gear sets controlled to provide at least eight forward speedratios and at least one reverse speed ratio.

The transmission family of the present invention has three planetarygear sets, each of which includes a first, second and third member,which members may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order.

In referring to the first, second and third gear sets in thisdescription and in the claims, these sets may be counted “first” to“third” in any order in the drawing (i.e., left to right, right to left,etc.). Additionally, the first, second or third members of each gear setmay be counted “first” to “third” in any order in the drawing (i.e., topto bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

An interconnecting member continuously connects the planet carrierassembly member of the first planetary gear set with the planet carrierassembly member of the second planetary gear set and with the ring gearmember of the third planetary gear set.

The sun gear member of the first planetary gear set is continuouslyconnected with the stationary member (transmission housing/casing).

The output member is continuously connected with the planet carrierassembly member of the third planetary gear set.

A first torque transmitting device, such as a brake, selectivelyconnects the ring gear member of the second planetary gear set with astationary member (transmission housing/casing).

A second torque transmitting device, such as a clutch, selectivelyconnects the ring gear member of the first planetary gear set with thering gear member of the second planetary gear set.

A third torque transmitting device, such as a clutch, selectivelyconnects the sun gear member of the second planetary gear set with thesun gear member of the third planetary gear set.

A fourth torque transmitting device, such as a clutch, selectivelyconnects the sun gear member of the second planetary gear set with theplanet carrier assembly member of the third planetary gear set.

A fifth torque transmitting device, such as a clutch, selectivelyconnects the ring gear member of the second planetary gear set with theinput member.

A sixth torque transmitting device, such as a clutch, selectivelyconnects the sun gear member of the third planetary gear set with theinput member.

The six torque-transmitting devices are selectively engageable incombinations of three to yield eight forward speed ratios and onereverse speed ratio.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is schematic representation of the powertrain of FIG. 1 adepicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes three planetary gear sets20, 30 and 40.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the sun gear member 22 and the ring gear member 24.

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37, 38 rotatablymounted on a carrier member 39. The pinion gears 38 are disposed inmeshing relationship with the ring gear member 34, and the pinion gears37 are disposed in meshing relationship with both the sun gear member 32and the respective pinion gear member 38.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47 mounted on acarrier member 49 and disposed in meshing relationship with both thering gear member 44 and the sun gear member 42.

The planetary gear arrangement also includes five torque-transmittingdevices 50, 52, 54, 55, 56 and 57. The torque-transmitting device 50 isa stationary-type torque-transmitting device, commonly termed brake orreaction clutch. The torque-transmitting devices 52, 54, 55, 56 and 57are rotating-type torque-transmitting devices, commonly termed clutches.

The output member 19 is continuously connected with the planet carrierassembly member 46 of the planetary gear set 40. The sun gear member 22of the planetary gear set 20 is continuously connected with thetransmission housing 60.

An interconnecting member 70 continuously connects the planet carrierassembly member 26 of the planetary gear set 20 with the planet carrierassembly member 36 of the planetary gear set 30 and with the ring gearmember 44 of the planetary gear set 40.

A first torque transmitting device, such as brake 50, selectivelyconnects the ring gear member 34 of the planetary gear set 30 with thetransmission housing 60. A second torque transmitting device, such asclutch 52, selectively connects the ring gear member 24 of the planetarygear set 20 with the ring gear member 34 of the planetary gear set 30. Athird torque transmitting device, such as clutch 54, selectivelyconnects the sun gear member 32 of the planetary gear set 30 with thesun gear member 42 of the planetary gear set 40. A fourth torquetransmitting device, such as clutch 55, selectively connects the sungear member 32 of the planetary gear set 30 with the planet carrierassembly member 46 of the planetary gear set 40. A fifth torquetransmitting device, such as clutch 56, selectively connects the ringgear member 34 of the planetary gear set 30 with the input member 17. Asixth torque transmitting device, such as clutch 57, selectivelyconnects the sun gear member 42 of the planetary gear set 40 with theinput member 17.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting devices are selectively engaged incombinations of three to provide at least eight forward speed ratios andat least one reverse speed ratio, all with single transition shifts.

As set forth above, the engagement schedule for the torque-transmittingdevices is shown in the truth table of FIG. 1 b. The chart of FIG. 1 bdescribes the ratio steps that are attained in the above describedtransmission. For example, the step ratio between the first and secondforward speed ratios is 1.68, while the step ratio between the reversespeed ratio and first forward ratio is −0.54.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format. A lever diagram is aschematic representation of the components of a mechanical device suchas an automatic transmission. Each individual lever represents aplanetary gearset, wherein the three basic mechanical components of theplanetary gear are each represented by a node. Therefore, a single levercontains three nodes: one for the sun gear member, one for the planetgear carrier member, and one for the ring gear member. The relativelength between the nodes of each lever can be used to represent thering-to-sun ratio of each respective gearset. These lever ratios, inturn, are used to vary the gear ratios of the transmission in order toachieve appropriate ratios and ratio progression. Mechanical couplingsor interconnections between the nodes of the various planetary gear setsare illustrated by thin, horizontal lines and torque transmittingdevices such as clutches and brakes are presented as interleavedfingers. If the device is a brake, one set of the fingers is grounded.Further explanation of the format, purpose and use of lever diagrams canbe found in SAE Paper 810102, authored by Benford, Howard and Leising,Maurice, “The Lever Analogy: A New Tool in Transmission Analysis”, 1981,which is hereby fully incorporated by reference.

The powertrain 10 includes an input member 17 continuously connectedwith the engine 12, and output member 19 continuously connected with thefinal drive mechanism 16, a first planetary gear set 20A having threenodes: a first node 22A, a second node 26A and a third node 24A; asecond planetary gear set 30A having three nodes: a first node 32A, asecond node 36A and a third node 34A; and a third planetary gear set 40Ahaving a first node 42A, a second node 46A and a third node 44A.

The output member 19 is continuously connected with the node 46A. Thenode 22A is continuously connected with the transmission housing 60.

The node 26A is continuously connected with the node 36A and the node44A.

A first torque-transmitting device, such as brake 50, selectivelyconnects the node 34A with the transmission housing 60. A secondtorque-transmitting device, such as clutch 52, selectively connects thenode 24A with the node 34A. A third torque-transmitting device, such asclutch 54, selectively connects the node 32A with the node 42A. A fourthtorque-transmitting device, such as clutch 55, selectively connects thenode 32A with the node 46A. A fifth torque-transmitting device, such asclutch 56, selectively connects the node 34A with the input member 17. Asixth torque-transmitting device, such as clutch 57, selectivelyconnects the node 42A with the input member 17.

To establish ratios, three torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row in FIG. 1 b. For example, to establishthe reverse gear, the brake 50, clutch 54 and clutch 57 are engaged. Thebrake 50 engages the node 34A with the transmission housing 60. Theclutch 54 engages the node 32A with the node 42A. The clutch 57 engagesthe node 42A with the input member 17. Likewise, the eight forward speedratios are achieved through different combinations of clutch engagementsas per FIG. 1 b.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second and third planetary gear sets each having first,second and third members; an interconnecting member continuouslyconnecting said second member of said first planetary gear set with saidsecond member of said second planetary gear set and with said thirdmember of said third planetary gear set; said first member of said firstplanetary gear set being continuously connected with a stationarymember; and six torque-transmitting devices with each of said torquetransmitting devices configured for selectively interconnecting saidmembers of said planetary gear sets with at least one of said stationarymember, said input member, and another of said members of said planetarygear sets, said six torque-transmitting devices being engaged incombinations of three to establish at least eight forward speed ratiosand at least one reverse speed ratio between said input member and saidoutput member.
 2. The transmission defined in claim 1, wherein one ofsaid six torque-transmitting device comprises a brake, and the others ofsaid six torque-transmitting devices comprise clutches.
 3. Thetransmission of claim 1, wherein said first, second and third members ofsaid first, second and third planetary gear sets each comprise a sungear member, a planet carrier assembly member and a ring gear member,respectively.
 4. The transmission of claim 1, wherein said output memberis continuously interconnected with said second member of said thirdplanetary gear set.
 5. The transmission of claim 1, wherein a first ofsaid six torque-transmitting devices is operable for selectivelyconnecting said third member of said second planetary gear set with saidstationary member.
 6. The transmission of claim 5, wherein a second ofsaid six torque-transmitting devices is operable for selectivelyconnecting said third member of said first planetary gear set with saidthird member of said second planetary gear set.
 7. The transmission ofclaim 6, wherein a third of said six torque-transmitting devices isoperable for selectively connecting said first member of said secondplanetary gear set with said first member of said third planetary gearset.
 8. The transmission of claim 7, wherein a fourth of said sixtorque-transmitting devices is operable for selectively connecting saidfirst member of said second planetary gear set with said second memberof said third planetary gear set.
 9. The transmission of claim 8,wherein a fifth of said six torque-transmitting devices is operable forselectively connecting said third member of said second planetary gearset with said input member.
 10. The transmission of claim 9, wherein asixth of said six torque-transmitting devices is operable forselectively connecting said first member of said third planetary gearset with said input member.
 11. A multi-speed transmission comprising:an input member; an output member; first, second and third planetarygear sets each having first, second and third members; aninterconnecting member continuously connecting said second member ofsaid first planetary gear set with said second member of said secondplanetary gear set and with said third member of said third planetarygear set; said first member of said first planetary gear set beingcontinuously connected with a stationary member; said output memberbeing continuously connected with said second member of said thirdplanetary gear set; a first torque-transmitting device selectivelyconnecting said third member of said second planetary gear set with saidstationary member; a second torque-transmitting device selectivelyconnecting said third member of said first planetary gear set with saidthird member of said second planetary gear set; a thirdtorque-transmitting device selectively connecting said first member ofsaid second planetary gear set with said first member of said thirdplanetary gear set; a fourth torque-transmitting device selectivelyconnecting said first member of said second planetary gear set with saidsecond member of said third planetary gear set; a fifthtorque-transmitting device selectively connecting said third member ofsaid second planetary gear set with said input member; a sixthtorque-transmitting device selectively connecting said first member ofsaid third planetary gear set with said input member; and said sixtorque-transmitting devices being engaged in combinations of three toestablish at least eight forward speed ratios and at least one reversespeed ratio between said input member and said output member.
 12. Amulti-speed transmission comprising: an input member; an output member;first, second and third planetary gear sets each having a sun gearmember, planet carrier assembly member and ring gear member; said outputmember being continuously interconnected with said planet carrierassembly member of said third planetary gear set; said sun gear memberof said first planetary gear set being continuously connected with astationary member; an interconnecting member continuously connectingsaid planet carrier assembly member of said first planetary gear setwith said planet carrier assembly member of said second planetary gearset and with said ring gear member of said third planetary gear set; afirst torque-transmitting device selectively connecting said ring gearmember of said second planetary gear set with said stationary member; asecond torque-transmitting device selectively connecting said ring gearmember of said first planetary gear set with said ring gear member ofsaid second planetary gear set; a third torque-transmitting deviceselectively connecting said sun gear member of said second planetarygear set with said sun gear member of said third planetary gear set; afourth torque-transmitting device selectively connecting said sun gearmember of said second planetary gear set with said planet carrierassembly member of said third planetary gear set; a fifthtorque-transmitting device selectively connecting said ring gear memberof said second planetary gear set with said input member; a sixthtorque-transmitting device selectively connecting said sun gear memberof said third planetary gear set with said input member; saidtorque-transmitting devices being engaged in combinations of three toestablish at least eight forward speed ratios and at least one reversespeed ratio between said input member and said output member.